The present invention relates to two new types of hyperbranched benzazole polymers.
Although aromatic-heterocyclic rigid-rod polybenzazoles such as polybenzobisthiazole (PBZT), polybenzobisoxazole (PBO), and polybenzobisimidazole (PBI) possess excellent thermal and mechanical properties, as well as interesting optical and electronic characteristics, their inherent insolubility in common organic solvents limits their applications. They are only soluble in strong acids such as methanesulfonic acid (MSA), trifluoromethanesulfonic acid (TFMSA), and sulfonic acid. These polymers, in general, are prepared from polycondensation of the respective monomers in mild acid such as polyphosphoric acid (PPA, 83% assay) at elevated temperature around 180° C.

On the other hand, non-linear macromolecules such as dendrimers and hyperbranched polymers are attracting considerable amount of attention primarily because of their distinctly different properties compared to their linear counterparts. For example, they have better solubility and compared to their linear analogs. Although dendrimers have precisely controlled structures and unique properties, their preparations generally involve tedious, multi-step sequences that are not practical in mass production. Synthesis of a hyperbranched polymer, on the other hand, is a one-pot process. Large quantities of hyperbranched polymers can be easily produced from ABx (x≧2) monomers. In addition, there are important characteristics of hyperbranched polymers and dendrimers such as low viscosity and endgroup-controlled physical properties are quite similar. Therefore, hyperbranched polymers are better suited for the practical applications. Perhaps, an important disadvantage associated with a particular hyperbranched polymer is that the synthesis of its ABx monomer often-time still involves a good number of reaction steps from commercially available starting materials.
Therefore, to be more economically competitive, a promising approach entails direct syntheses of hyperbranched polymers for high temperature applications from commercially available A3 and B2 or A2 and B3. Although a number of hyperbranched polymers have been synthesized via either an A3+B2 or an A2+B3 polycondensation processes, these processes do have some inherent difficulty in preventing premature gelation as predicted by Carother's and statistical mechanics equations. Thus, an important key to the success of such an approach is to be able to control the reaction parameters such as the monomer concentrations and their time-dependent stoichiometric ratio, and stop the reaction before the gelation starts.
Accordingly, it is an object of the present invention to provide novel hyperbranched benzobisthiazole and bibenzothiazole polymers generated from a A3+B2 polymerization in poly(phosphoric acid).
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.